This is a joke, right? There are many different forms of drugs, and they could look like completely legal things in a bag. It's a little hard to tell with how general your question is.
drugs look like pills and other medicines poo
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.
A substance not containing an illegal drug or controlled substance.
There are literally hundreds. You can look them up on the DEA Schedule I of the controlled substances list.
Look up "Schedule I controlled substances". That list contains all drugs that are illegal and also (according to the federal government at least) have no medical value. If you have any other controlled substance in your possession when you are not prescribed it, that is also illegal.
You can look for them on a site like amazon.com or ebay.com
Drug screenings look for all hardcore drugs such as meth, coke, crack, marijuana, etc.
tums
Take drugs.
There are tremendous amounts of different drugs -- some are good for the body, such as drugs to treat blood pressure or diabetes; some are bad for the body, such as illegal drugs -- they're illegal because they kill people! -- and some are so-so, such as caffeine and nicotine, which can be very harmful but most people do use them. different drugs have different effects. most get you high. stimulants like cocaine and caffeine(its not illegal!) speed up your heart rate, breathing rate, bloodpressure goes up, and things like that. hallucinigens make you see things that arent really there. methamphetamine makes you sweat, it makes your pupils look ragged and things li,e that.
It is NEVER old enough. Not only are drugs illegal and you can go to prison, but you can die from using drugs or ruin your body through drug use. I am sure you have dreams about what you want to do with your life, but if you use drugs those dreams go away. Many jobs also will not hire people with drug convictions or look like they use.
Nope. Look at how well DRUG control works. They have been illegal for many years. You can still get drugs.