Homemade drug tests are very popular right now because marijuana is still illegal in the United States in most states and even in states where weed is legalized or decriminalized testing positive on drug tests can still have consequences and disqualify you from many federal government benefit programs.
Obviously, that is not good and can potentially cost thousands of dollars in lost money so you need to be sure your at-home drug test is accurate. Fortunately, technology has advanced to the point that delivered to home drug tests which are only around 30-50 dollars can accurately test for traces of THC left in your body to the degree of accuracy of a government drug test. Check out exit-5 reviews for the best way to do drug tests at home. Since the government wants to have a monopoly on drug tests for obvious reasons, in-home drug tests are sort of in a legal grey zone.
The laws surrounding the legality of these in-home drug tests is weird and vague, and the government makes it difficult for one to be shipped to you. The United States Postal Service will confiscate and drug test shipment it finds in its shipments so even though USPS is usually the cheapest carrier, it is usually better to use a private courier service like DHL, Fedex, or UPS to not have your drug test confiscated by the police. The online ordering process is also a lot more complicated than normal online shopping because of the government regulations in this area. You may have to route the payment through an external foreign service, which might seem sketchy and take more time than the traditional straight to credit card payments in the US.
This is because of most large credit card companies and even paypal block payments to companies that sell drug tests to say in the legal green zone.