Benzodiazepines are generally regarded as safe drugs, and are widely used in the clinical treatment of anxiety (and other mental conditions). Overdose of benzodiazepine leads to sedation and hypnosis, without resulting in death. However, benzodiazepines combined with alcohol removes the progression towards death and coma. This is due to the combination with other nervous system depressants.
Tolerance can, over time, build up to benzodiazepines. This results in needing higher and higher doses to elicit the same effect.
A physical dependence is also possible with benzodiazepines. On withdrawing from the drug, insomnia, anxiety, and convulsions are not uncommon.
Other drugs, including propranolol and SSRIs can be used to treat generalised anxiety, and these tend to have fewer side effects due to their specificity. However, they may not work for all individuals, and so benzodiazepines are still used (but with an understanding of the risks involved).