Gunson - who has headed the agency's prescription medicines division for 13 years - becomes chairman and majority shareholder, having snapped up 51 per cent of the agency's shares from Munro.
Julie Flexen, who has led the consumer practice for nine years, becomes sole MD, with director of prescription medicines Sarah Hart becoming deputy MD.
Gunson, who this week pledged to double annual turnover from the current £5.2m within five years, said: 'We want to be seen as a lighthouse in terms of remaining independent. We have had our suitors but we want to be independent ambassadors.'
Gunson said he envisaged opportunities for business in fields including 'strategic consultancy', NHS stakeholder work and promoting wellbeing products.