Meth is dangerously addictive and it powerfully damages your brain and body. Long-term effects of this drug are ugly and scary. Meth causes weight loss, tooth loss and massive itching due to crystalized meth that accumulates under your skin...causing nasty scabs and sores on your skin and face. A range of psychotic behaviors, including paranoia, anxiety, extreme violence, hallucinations, and delusions are often displayed by meth users. The most common meth delusion is the feeling of insects crawling under the skin (once again, due to crystalized meth).