This traditional Indian yogurt-based drink hails from the pre-refrigeration era when Punjabi farmers mixed their milk with sugar and curd and kept the concoction in clay pots. Lassi is often flavored with a variety of fresh herbs, different spices, fruits, and floral essences.
Today, it is typically mixed with ice and served as an accompaniment to hot and spicy dishes, as it provides refreshment for the palate and soothes the body, especially on hot summer days. Sweet lassi is called metha lassi and it often contains ginger, mint, rosewater, cardamom, and exotic fruits like mango.
Namkeen lassi is the salty version of lassi, typically flavored with ground black pepper, garlic, and roasted cumin seeds. The traditional namkeen (or salty) form of lassi is more common in the Indian subcontinent. It is prepared by blending dahi (yogurt) with water with added salt. The resulting beverage is known as salted lassi.
Another popular variety is the so-called bhang lassi. Bhang lassi is a cannabis-infused drink that contains bhang, a liquid derivative of cannabis, which has effects similar to other eaten forms of cannabis. It is legal in many parts of India. Uttar Pradesh is known to have licensed bhang shops, and in many places, one can buy bhang products and drink bhang lassis. It is mostly consumed during exuberant Indian festivals like Maha Shivaratri.
According to en.wikipedia.org