Possible side effects of Clenbuterol include restlessness, palpitations, tremor (involuntary trembling of fingers), headache, increased per-spiration, insomnia, possible muscle spasms, increased blood pres-sure, and nausea. Note that these side effects are of a temporary nature and usually subside after 8-10 days, despite continuation of the product.I tend to shake myself on clen give it a few days if it persists drop the dosage down everyones diferent your body may not handle as much as your taking.