The group of drugs which are less toxic in nature than visha and not so lethal and produces certain toxic symptoms on consumption or administration is called as Upavisha .

Sankhya (Number) of Upavisha– The number of upavisha varies in different samhita.
Rasarnava-5
Rasasanket kalik-6
Rasendra chudamani, Rasaratna samucchaya, Rasendra chintamani, Bhavaprakasha, Ayurveda prakasha, Yogratnakar, Rasendra sarasagraha-7
Rasatarangini-11

The Books cover all details about these Upvisha with all toxic symptoms on human body with remedies for that as antidote of toxin.

Upavisha-

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1. Vishatinduka-Kupilu
2. Ahiphena
3. Rechakam-jayapala
4. Dhatura-
5. Vijaya-Bhanga
6. Gunja
7. Bhallataka
8. Arka
9. Snuhi
10. Langali
11. Karvirya

these all medicines have there own toxic symptoms with antidote of toxin analysis

Shodhana of Upavisha
There are various methods are prescribed in Samhitas for purification of Upa vishas. They are –
1. Gomutra Nimajjana – The visha dravyas soaked in cow’s urine for some prescribed period of time.
2. Swedana – Visha dravyas should boiled for a given time in different liquids such as cow’s milk, cow’s urine, goat’s milk, vegetables extracts, kanika etc
3. Bharana – frying of visha dravya with ghee or without ghee.
4. Bhavana – Trituration of visha dravya with vegetable extracts
5. Nish shehana – reducing of oily contents
6. Kshalana – washing of visha dravya with hot water
7. Nistvacikarana – Decortications

Theses Shuddhikaran procedure not reduce toxins but also helps in work like antidote of toxin