GW Pharmaceuticals, which is developing the world's first cannabis-based medicine for pain relief, has raised stg£25m through an initial public offering.
Chief executive Geoffrey Guy will see his paper fortune valued at stg£47m when the company floats on the junior AIM stock market next Thursday.
GW, founded by Dr Guy three years ago, increased the number of new shares it offered to institutions following strong demand.
It had originally hoped to raise £16m of fresh funds.
It will plough the cash into clinical trials of its treatments for multiple sclerosis (MS) and cancer pain.
If the trials are a success, GW hopes to apply for regulatory approval from Britain's Medicines Control Agency in 2003 and begin selling the drugs in early 2004.
GW Pharmaceuticals currently produces 15 tonnes of cannabis in secret locations in the UK each year, and aims to increase this to 100 tonnes.
The company claims its drugs, which are sprayed on to the tongue, don't produce a high because they're made from processed marijuana.
It says early clinical trials of the drug in the UK have shown effectiveness in treating symptoms of multiple sclerosis, arthritis and cancer.