illicit drugs are control drugs while licit are drugs that are not control
illicit-unlawful.
Licit drugs are drugs that are legal.
The root word of "illicit" is "licit," which means legal or permissible. "Illicit" means something that is not legally allowed or forbidden by law.
The government of each country makes their own decisions on these matters. Usually it is down to a combination of the health and legal ministries.
Medical drugs are prescribed for a particular medical need- such as infection control, pain relief, etc. Recreational drugs are taken for fun. Medical drugs are sometimes used as recreational drugs.
There is an extremely long list of licit drugs that look like illicit drugs to some drug tests. Poppyseeds will look like opiates (probably since they have opiates in them), most of the new pain relievers like naproxen and ibuprofen look like weed, and Alka-Seltzer looks like speed. Use http://www.askdocweb.com/falsepositives.html to see what crosses with what.
Combining drugs leads to drug synergy, where the combined effect is greater than the sum of the individual effects. Since we're in the illicit-drugs realm rather than the licit one (where a doctor might prescribe two separate antibiotics to exploit synergism to kill a really nasty infection), one famous synergism is mixing booze and barbiturates, which used to be a popular way for women to attempt suicide.
Combing drugs can lead to an adverse reaction in the body. This can cause nausea, vomiting, dizziness, or even cause a person to pass out. Combing drugs should not be done without doctor's okay.
The prefix form for licit is il-.
Legal, lawful, permissible, and authorized are synonyms of licit.
Why not? However, it should only be between the girl and her husband per licit marriage.