Richard Davis, 53, was diagnosed with a non-malignant pituitary gland tumour in 1989.
The High Court in London heard that Mr Davis, who founded magazine publishers, Parkway Publications Ltd, became bankrupt with criminal convictions and no business.
Novartis Pharmaceuticals (UK) Ltd; Camden and Islington Health Authority (sued as managers of Middlesex Hospital where Mr Davis was treated) and consultant Professor Howard Saul Jacobs, now retired, all deny liability.
Until 1993, Mr Davis, from Mill Hill in London, was prescribed a class of drugs known as dopamine agonists.
Psychiatric effects
His counsel, Roger Henderson QC, said these were known to have psychiatric effects on some patients.
Initially prescribed a drug called bromocriptine, which goes under the proprietary label Parlodel, he also took part in clinical trials of an experimental drug - known as CV205-502 - which had at that time not been licensed for sale in the UK.
Bromocriptine also brought on a "marked and sometimes dramatic increase in libido" that made his sexual behaviour "incontinent and inappropriate", said Mr Henderson.
Mr Davis was convicted of dishonesty on two occasions, in December 1992 and March 1995 and was made bankrupt in 1993.
The hearing is expected to last up to eight weeks.