Cyanide in a very large dose!
Yes. X-rays can alter DNA, and DNA can be altered by scientists.
No, you can't "alter" DNA with such crude methods, only destroy it...
All drugs will alter your urine
There are no drugs that I am aware of that can change your DNA. And if your the same person that asked how accurate DNA tests are, they are very accurate. There is a very small chance that one can be wrong, but even a high paid lawyer couldn't get you out of trouble if your DNA is used. If you did something wrong (get someone nocked up maybe?) and DNA is involved, you might as well admit to it.
The environment, viruses, and scientists have the ability to alter DNA. These alterations may potentially be passed on to future generations.
A person would not be able to alter a DNA test. Doctors performing DNA tests take very careful precautions to prevent the tests from being altered.
Chemical substance that alter perceptions and mood are called Psychoactive Drugs.
cells
No way, man. Smoking weed does not alter your DNA, no matter how much you think you smoke.
yes
Psychoactive (psychotropic) drugs alter perceptions and moods. One class of drugs which causes vast changes in perception is psychedelics.