Thallium Metallicum is a homeopathic remedy prepared from the rare metal thallium which is formed as a residue after distillation of selenium. It is best suited for the following cases-

Nervous system

Paralysis, especially of the lower limbs. 
Painful and inflamed nerves with electric shock like pains, as in nerve inflammation or chronic myelitis.
Nerve affections causing muscles to atrophy.
Trembling of limbs and a crawling sensation in limbs.

Hair- Alopecia (hairfall) after an acute attack of any disease has occurred. 

Glands- Diseases of the thyroid and adrenal glands.

Dose- As prescribed by physician. Can be taken along with allopathic medicines. 

Precautions: 

Maintain half an hour gap between food/drink/any other medicines and homeopathic medicine.
Avoid any strong smell in the mouth while taking medicine e.g. camphor, garlic, onion, coffee, hing.

Side effects- none reported

Use under medical supervision