Justice Stevens delivered the opinion of the Court.

California is one of at least nine States that authorize the use of marijuana for medicinal purposes. The question presented in this case is whether the power vested in Congress by Article I, §8, of the Constitution "[t]o make all Laws which shall be necessary and proper for carrying into Execution" its authority to "regulate Commerce with foreign Nations, and among the several States" includes the power to prohibit the local cultivation and use of marijuana in compliance with California law.

California has been a pioneer in the regulation of marijuana. In 1913, California was one of the first States to prohibit the sale and possession of marijuana, and at the end of the century, California became the first State to authorize limited use of the drug for medicinal purposes. In 1996, California voters passed Proposition 215, now codified as the Compassionate Use Act of 1996. The proposition was designed to ensure that "seriously ill" residents of the State have access to marijuana for medical purposes, and to encourage Federal and State Governments to take steps towards ensuring the safe and affordable distribution of the drug to patients in need. The Act creates an exemption from criminal prosecution for physicians, as well as for patients and primary caregivers who possess or cultivate marijuana for medicinal purposes with the recommendation or approval of a physician. A "primary caregiver" is a person who has consistently assumed responsibility for the housing, health, or safety of the patient.

Respondents Angel Raich and Diane Monson are California residents who suffer from a variety of serious medical conditions and have sought to avail themselves of medical marijuana pursuant to the terms of the Compassionate Use Act. They are being treated by licensed, board-certified family practitioners, who have concluded, after prescribing a host of conventional medicines to treat respondents' conditions and to alleviate their associated symptoms, that marijuana is the only drug available that provides effective treatment. Both women have been using marijuana as a medication for several years pursuant to their doctors' recommendation, and both rely heavily on cannabis to function on a daily basis. Indeed, Raich's physician believes that forgoing cannabis treatments would certainly cause Raich excruciating pain and could very well prove fatal.

Respondent Monson cultivates her own marijuana, and ingests the drug in a variety of ways including smoking and using a vaporizer. Respondent Raich, by contrast, is unable to cultivate her own, and thus relies on two caregivers, litigating as "John Does," to provide her with locally grown marijuana at no charge. These caregivers also process the cannabis into hashish or keif, and Raich herself processes some of the marijuana into oils, balms, and foods for consumption.

On August 15, 2002, county deputy sheriffs and agents from the federal Drug Enforcement Administration (DEA) came to Monson's home. After a thorough investigation, the county officials concluded that her use of marijuana was entirely lawful as a matter of California law. Nevertheless, after a 3-hour standoff, the federal agents seized and destroyed all six of her cannabis plants.

Respondents thereafter brought this action against the Attorney General of the United States and the head of the DEA seeking injunctive and declaratory relief prohibiting the enforcement of the federal Controlled Substances Act (CSA) to the extent it prevents them from possessing, obtaining, or manufacturing cannabis for their personal medical use. In their complaint and supporting affidavits, Raich and Monson described the severity of their afflictions, their repeatedly futile attempts to obtain relief with conventional medications, and the opinions of their doctors concerning their need to use marijuana. Respondents claimed that enforcing the CSA against them would violate the Commerce Clause, the Due Process Clause of the Fifth Amendment, the Ninth and Tenth Amendments of the Constitution, and the doctrine of medical necessity.

The District Court denied respondents' motion for a preliminary injunction.... A divided panel of the Court of Appeals for the Ninth Circuit reversed and ordered the District Court to enter a preliminary injunction. The court found that respondents had "demonstrated a strong likelihood of success on their claim that, as applied to them, the CSA is an unconstitutional exercise of Congress' Commerce Clause authority."

The majority placed heavy reliance on our decisions in United States v. Lopez, 514 U. S. 549 (1995), and United States v. Morrison, 529 U. S. 598 (2000), as interpreted by recent Circuit precedent, to hold that this separate class of purely local activities was beyond the reach of federal power....

The obvious importance of the case prompted our grant of certiorari. The case is made difficult by respondents' strong arguments that they will suffer irreparable harm because, despite a congressional finding to the contrary, marijuana does have valid therapeutic purposes. The question before us, however, is not whether it is wise to enforce the statute in these circumstances; rather, it is whether Congress' power to regulate interstate markets for medicinal substances encompasses the portions of those markets that are supplied with drugs produced and consumed locally. Well-settled law controls our answer. The CSA is a valid exercise of federal power, even as applied to the troubling facts of this case. We accordingly vacate the judgment of the Court of Appeals....

II

Marijuana itself was not significantly regulated by the Federal Government until 1937 when accounts of marijuana's addictive qualities and physiological effects, paired with dissatisfaction with enforcement efforts at state and local levels, prompted Congress to pass the Marihuana Tax Act. Like the Harrison Act, the Marihuana Tax Act did not outlaw the possession or sale of marijuana outright. Rather, it imposed registration and reporting requirements for all individuals importing, producing, selling, or dealing in marijuana, and required the payment of annual taxes in addition to transfer taxes whenever the drug changed hands....

Then in 1970, after declaration of the national "war on drugs," federal drug policy underwent a significant transformation.... Prompted by a perceived need to consolidate the growing number of piecemeal drug laws and to enhance federal drug enforcement powers, Congress enacted the Comprehensive Drug Abuse Prevention and Control Act....

Congress devised a closed regulatory system making it unlawful to manufacture, distribute, dispense, or possess any controlled substance except in a manner authorized by the CSA. The CSA categorizes all controlled substances into five schedules. The drugs are grouped together based on their accepted medical uses, the potential for abuse, and their psychological and physical effects on the body...

In enacting the CSA, Congress classified marijuana as a Schedule I drug. This preliminary classification was based, in part, on the recommendation of the Assistant Secretary of HEW "that marihuana be retained within schedule I at least until the completion of certain studies now underway." Schedule I drugs are categorized as such because of their high potential for abuse, lack of any accepted medical use, and absence of any accepted safety for use in medically supervised treatment. ...By classifying marijuana as a Schedule I drug, as opposed to listing it on a lesser schedule, the manufacture, distribution, or possession of marijuana became a criminal offense, with the sole exception being use of the drug as part of a Food and Drug Administration pre-approved research study. Despite considerable efforts to reschedule marijuana, it remains a Schedule I drug.

III

Respondents in this case do not dispute that passage of the CSA, as part of the Comprehensive Drug Abuse Prevention and Control Act, was well within Congress' commerce power. Nor do they contend that any provision or section of the CSA amounts to an unconstitutional exercise of congressional authority. Rather, respondents' challenge is actually quite limited; they argue that the CSA's categorical prohibition of the manufacture and possession of marijuana as applied to the intrastate manufacture and possession of marijuana for medical purposes pursuant to California law exceeds Congress' authority under the Commerce Clause.

In assessing the validity of congressional regulation, none of our Commerce Clause cases can be viewed in isolation. As charted in considerable detail in United States v. Lopez, our understanding of the reach of the Commerce Clause, as well as Congress' assertion of authority thereunder, has evolved over time. The Commerce Clause emerged as the Framers' response to the central problem giving rise to the Constitution itself: the absence of any federal commerce power under the Articles of Confederation. For the first century of our history, the primary use of the Clause was to preclude the kind of discriminatory state legislation that had once been permissible. Then, in response to rapid industrial development and an increasingly interdependent national economy, Congress "ushered in a new era of federal regulation under the commerce power," beginning with the enactment of the Interstate Commerce Act in 1887 and the Sherman Antitrust Act in 1890.

Cases decided during that "new era," which now spans more than a century, have identified three general categories of regulation in which Congress is authorized to engage under its commerce power. First, Congress can regulate the channels of interstate commerce. Perez v. United States (1971). Second, Congress has authority to regulate and protect the instrumentalities of interstate commerce, and persons or things in interstate commerce. Third, Congress has the power to regulate activities that substantially affect interstate commerce. NLRB v. Jones & Laughlin Steel Corp. (1937). Only the third category is implicated in the case at hand.

Our case law firmly establishes Congress' power to regulate purely local activities that are part of an economic "class of activities" that have a substantial effect on interstate commerce. Wickard v. Filburn (1942). As we stated in Wickard, "even if appellee's activity be local and though it may not be regarded as commerce, it may still, whatever its nature, be reached by Congress if it exerts a substantial economic effect on interstate commerce."  We have never required Congress to legislate with scientific exactitude. When Congress decides that the " 'total incidence' " of a practice poses a threat to a national market, it may regulate the entire class.

Our decision in Wickard is of particular relevance. In Wickard, we upheld the application of regulations promulgated under the Agricultural Adjustment Act of 1938 which were designed to control the volume of wheat moving in interstate and foreign commerce in order to avoid surpluses and consequent abnormally low prices. The regulations established an allotment of 11.1 acres for Filburn's 1941 wheat crop, but he sowed 23 acres, intending to use the excess by consuming it on his own farm. Filburn argued that even though we had sustained Congress' power to regulate the production of goods for commerce, that power did not authorize "federal regulation [of] production not intended in any part for commerce but wholly for consumption on the farm." Justice Jackson's opinion for a unanimous Court rejected this submission. He wrote:

"The effect of the statute before us is to restrict the amount which may be produced for market and the extent as well to which one may forestall resort to the market by producing to meet his own needs. That appellee's own contribution to the demand for wheat may be trivial by itself is not enough to remove him from the scope of federal regulation where, as here, his contribution, taken together with that of many others similarly situated, is far from trivial."

Wickard thus establishes that Congress can regulate purely intrastate activity that is not itself "commercial," in that it is not produced for sale, if it concludes that failure to regulate that class of activity would undercut the regulation of the interstate market in that commodity.

The similarities between this case and Wickard are striking. Like the farmer in Wickard, respondents are cultivating, for home consumption, a fungible commodity for which there is an established, albeit illegal, interstate market. Just as the Agricultural Adjustment Act was designed "to control the volume [of wheat] moving in interstate and foreign commerce in order to avoid surpluses ..." and consequently control the market price, id., at 115, a primary purpose of the CSA is to control the supply and demand of controlled substances in both lawful and unlawful drug markets.  In Wickard, we had no difficulty concluding that Congress had a rational basis for believing that, when viewed in the aggregate, leaving home-consumed wheat outside the regulatory scheme would have a substantial influence on price and market conditions. Here too, Congress had a rational basis for concluding that leaving home-consumed marijuana outside federal control would similarly affect price and market conditions.

More concretely, one concern prompting inclusion of wheat grown for home consumption in the 1938 Act was that rising market prices could draw such wheat into the interstate market, resulting in lower market prices. The parallel concern making it appropriate to include marijuana grown for home consumption in the CSA is the likelihood that the high demand in the interstate market will draw such marijuana into that market. While the diversion of homegrown wheat tended to frustrate the federal interest in stabilizing prices by regulating the volume of commercial transactions in the interstate market, the diversion of homegrown marijuana tends to frustrate the federal interest in eliminating commercial transactions in the interstate market in their entirety. In both cases, the regulation is squarely within Congress' commerce power because production of the commodity meant for home consumption, be it wheat or marijuana, has a substantial effect on supply and demand in the national market for that commodity.

Nonetheless, respondents suggest that Wickard differs from this case in three respects: (1) the Agricultural Adjustment Act, unlike the CSA, exempted small farming operations; (2) Wickard involved a "quintessential economic activity"--a commercial farm--whereas respondents do not sell marijuana; and (3) the Wickard record made it clear that the aggregate production of wheat for use on farms had a significant impact on market prices. Those differences, though factually accurate, do not diminish the precedential force of this Court's reasoning....

Respondents nonetheless insist that the CSA cannot be constitutionally applied to their activities because Congress did not make a specific finding that the intrastate cultivation and possession of marijuana for medical purposes based on the recommendation of a physician would substantially affect the larger interstate marijuana market. Be that as it may, we have never required Congress to make particularized findings in order to legislate, absent a special concern such as the protection of free speech. While congressional findings are certainly helpful in reviewing the substance of a congressional statutory scheme, particularly when the connection to commerce is not self-evident, and while we will consider congressional findings in our analysis when they are available, the absence of particularized findings does not call into question Congress' authority to legislate.

In assessing the scope of Congress' authority under the Commerce Clause, we stress that the task before us is a modest one. We need not determine whether respondents' activities, taken in the aggregate, substantially affect interstate commerce in fact, but only whether a "rational basis" exists for so concluding. Given the enforcement difficulties that attend distinguishing between marijuana cultivated locally and marijuana grown elsewhere, and concerns about diversion into illicit channels, we have no difficulty concluding that Congress had a rational basis for believing that failure to regulate the intrastate manufacture and possession of marijuana would leave a gaping hole in the CSA. Thus, as in Wickard, when it enacted comprehensive legislation to regulate the interstate market in a fungible commodity, Congress was acting well within its authority to "make all Laws which shall be necessary and proper" to "regulate Commerce ... among the several States." That the regulation ensnares some purely intrastate activity is of no moment. As we have done many times before, we refuse to excise individual components of that larger scheme....

Justice Scalia, concurring in the judgment.

Congress has undertaken to extinguish the interstate market in Schedule I controlled substances, including marijuana. The Commerce Clause unquestionably permits this. The power to regulate interstate commerce "extends not only to those regulations which aid, foster and protect the commerce, but embraces those which prohibit it." To effectuate its objective, Congress has prohibited almost all intrastate activities related to Schedule I substances--both economic activities (manufacture, distribution, possession with the intent to distribute) and noneconomic activities (simple possession). That simple possession is a noneconomic activity is immaterial to whether it can be prohibited as a necessary part of a larger regulation. Rather, Congress's authority to enact all of these prohibitions of intrastate controlled-substance activities depends only upon whether they are appropriate means of achieving the legitimate end of eradicating Schedule I substances from interstate commerce.

By this measure, I think the regulation must be sustained. Not only is it impossible to distinguish "controlled substances manufactured and distributed intrastate" from "controlled substances manufactured and distributed interstate," but it hardly makes sense to speak in such terms. Drugs like marijuana are fungible commodities....

Justice O'Connor, with whom The Chief Justice and Justice Thomas join as to all but Part III, dissenting.

We enforce the "outer limits" of Congress' Commerce Clause authority not for their own sake, but to protect historic spheres of state sovereignty from excessive federal encroachment and thereby to maintain the distribution of power fundamental to our federalist system of government. One of federalism's chief virtues, of course, is that it promotes innovation by allowing for the possibility that "a single courageous State may, if its citizens choose, serve as a laboratory; and try novel social and economic experiments without risk to the rest of the country." 

This case exemplifies the role of States as laboratories. The States' core police powers have always included authority to define criminal law and to protect the health, safety, and welfare of their citizens.  Exercising those powers, California (by ballot initiative and then by legislative codification) has come to its own conclusion about the difficult and sensitive question of whether marijuana should be available to relieve severe pain and suffering. Today the Court sanctions an application of the federal Controlled Substances Act that extinguishes that experiment, without any proof that the personal cultivation, possession, and use of marijuana for medicinal purposes, if economic activity in the first place, has a substantial effect on interstate commerce and is therefore an appropriate subject of federal regulation. In so doing, the Court announces a rule that gives Congress a perverse incentive to legislate broadly pursuant to the Commerce Clause--nestling questionable assertions of its authority into comprehensive regulatory schemes--rather than with precision. That rule and the result it produces in this case are irreconcilable with our decisions in Lopez and United States v. Morrison. Accordingly I dissent....

We must determine whether, under our precedents, the conduct is economic and, in the aggregate, substantially affects interstate commerce. Even if intrastate cultivation and possession of marijuana for one's own medicinal use can properly be characterized as economic, and I question whether it can, it has not been shown that such activity substantially affects interstate commerce. Similarly, it is neither self-evident nor demonstrated that regulating such activity is necessary to the interstate drug control scheme.

The Court's definition of economic activity is breathtaking. It defines as economic any activity involving the production, distribution, and consumption of commodities. And it appears to reason that when an interstate market for a commodity exists, regulating the intrastate manufacture or possession of that commodity is constitutional either because that intrastate activity is itself economic, or because regulating it is a rational part of regulating its market. Putting to one side the problem endemic to the Court's opinion--the shift in focus from the activity at issue in this case to the entirety of what the CSA regulates,--the Court's definition of economic activity for purposes of Commerce Clause jurisprudence threatens to sweep all of productive human activity into federal regulatory reach.

The Court uses a dictionary definition of economics to skirt the real problem of drawing a meaningful line between "what is national and what is local." It will not do to say that Congress may regulate noncommercial activity simply because it may have an effect on the demand for commercial goods, or because the noncommercial endeavor can, in some sense, substitute for commercial activity. Most commercial goods or services have some sort of privately producible analogue. Home care substitutes for daycare. Charades games substitute for movie tickets. Backyard or windowsill gardening substitutes for going to the supermarket. To draw the line wherever private activity affects the demand for market goods is to draw no line at all, and to declare everything economic. We have already rejected the result that would follow--a federal police power.

In Lopez and Morrison, we suggested that economic activity usually relates directly to commercial activity. The homegrown cultivation and personal possession and use of marijuana for medicinal purposes has no apparent commercial character. Everyone agrees that the marijuana at issue in this case was never in the stream of commerce, and neither were the supplies for growing it. (Marijuana is highly unusual among the substances subject to the CSA in that it can be cultivated without any materials that have traveled in interstate commerce.) Lopez makes clear that possession is not itself commercial activity. And respondents have not come into possession by means of any commercial transaction; they have simply grown, in their own homes, marijuana for their own use, without acquiring, buying, selling, or bartering a thing of value.

The Court suggests that Wickard, which we have identified as "perhaps the most far reaching example of Commerce Clause authority over intrastate activity," established federal regulatory power over any home consumption of a commodity for which a national market exists. I disagree. Wickard involved a challenge to the Agricultural Adjustment Act  which directed the Secretary of Agriculture to set national quotas on wheat production, and penalties for excess production. The AAA itself confirmed that Congress made an explicit choice not to reach--and thus the Court could not possibly have approved of federal control over--small-scale, noncommercial wheat farming. In contrast to the CSA's limitless assertion of power, Congress provided an exemption within the AAA for small producers. When Filburn planted the wheat at issue in Wickard, the statute exempted plantings less than 200 bushels (about six tons), and when he harvested his wheat it exempted plantings less than six acres. Wickard, then, did not extend Commerce Clause authority to something as modest as the home cook's herb garden. This is not to say that Congress may never regulate small quantities of commodities possessed or produced for personal use, or to deny that it sometimes needs to enact a zero tolerance regime for such commodities. It is merely to say that Wickard did not hold or imply that small-scale production of commodities is always economic, and automatically within Congress' reach.

Even assuming that economic activity is at issue in this case, the Government has made no showing in fact that the possession and use of homegrown marijuana for medical purposes, in California or elsewhere, has a substantial effect on interstate commerce. Similarly, the Government has not shown that regulating such activity is necessary to an interstate regulatory scheme. Whatever the specific theory of "substantial effects" at issue (i.e., whether the activity substantially affects interstate commerce, whether its regulation is necessary to an interstate regulatory scheme, or both), a concern for dual sovereignty requires that Congress' excursion into the traditional domain of States be justified.

That is why characterizing this as a case about the Necessary and Proper Clause does not change the analysis significantly. Congress must exercise its authority under the Necessary and Proper Clause in a manner consistent with basic constitutional principles.... Otherwise, the Necessary and Proper Clause will always be a back door for unconstitutional federal regulation....

There is simply no evidence that homegrown medicinal marijuana users constitute, in the aggregate, a sizable enough class to have a discernable, let alone substantial, impact on the national illicit drug market--or otherwise to threaten the CSA regime. Explicit evidence is helpful when substantial effect is not "visible to the naked eye."  And here, in part because common sense suggests that medical marijuana users may be limited in number and that California's Compassionate Use Act and similar state legislation may well isolate activities relating to medicinal marijuana from the illicit market, the effect of those activities on interstate drug traffic is not self-evidently substantial.

In this regard, again, this case is readily distinguishable from Wickard. To decide whether the Secretary could regulate local wheat farming, the Court looked to "the actual effects of the activity in question upon interstate commerce." Critically, the Court was able to consider "actual effects" because the parties had "stipulated a summary of the economics of the wheat industry." After reviewing in detail the picture of the industry provided in that summary, the Court explained that consumption of homegrown wheat was the most variable factor in the size of the national wheat crop, and that on-site consumption could have the effect of varying the amount of wheat sent to market by as much as 20 percent.  With real numbers at hand, the Wickard Court could easily conclude that "a factor of such volume and variability as home-consumed wheat would have a substantial influence on price and market conditions" nationwide. 

The Court recognizes that "the record in the Wickard case itself established the causal connection between the production for local use and the national market" and argues that "we have before us findings by Congress to the same effect." The Court refers to a series of declarations in the introduction to the CSA saying that (1) local distribution and possession of controlled substances causes "swelling" in interstate traffic; (2) local production and distribution cannot be distinguished from interstate production and distribution; (3) federal control over intrastate incidents "is essential to effective control" over interstate drug trafficking. These bare declarations cannot be compared to the record before the Court in Wickard....

III

We would do well to recall how James Madison, the father of the Constitution, described our system of joint sovereignty to the people of New York: "The powers delegated by the proposed constitution to the federal government are few and defined. Those which are to remain in the State governments are numerous and indefinite... . The powers reserved to the several States will extend to all the objects which, in the ordinary course of affairs, concern the lives, liberties, and properties of the people, and the internal order, improvement, and prosperity of the State."

Relying on Congress' abstract assertions, the Court has endorsed making it a federal crime to grow small amounts of marijuana in one's own home for one's own medicinal use. This overreaching stifles an express choice by some States, concerned for the lives and liberties of their people, to regulate medical marijuana differently. If I were a California citizen, I would not have voted for the medical marijuana ballot initiative; if I were a California legislator I would not have supported the Compassionate Use Act. But whatever the wisdom of California's experiment with medical marijuana, the federalism principles that have driven our Commerce Clause cases require that room for experiment be protected in this case. For these reasons I dissent.