"Altered States" by Paddy Chayefsky

Eddie Jessup is obsessed with his work. Emily is obsessed with Eddie, despite his blatant declaration that he will never love her or be as dedicated to her as he is to his work. A scientist in her own right, she marries him anyway. As Eddie delves further and further into his search for the ultimate connection to human consciousness through the use of a hallucinogenic potion from South America and a sensory deprivation tank, he changes physically, mentally, and spiritually. How exactly these changes happen and how they affect those around him makes for a great read. 

Published in 1978, the book is out of print. This copy is in very good condition but without its dust jacket. There is also an inscription written on the front endpaper. 

If you have seen the 1980 film of the same name, you will recognize much of the dialogue in the book. Chayefsky adapted his novel for the screenplay which was directed by Ken Russell and starred William Hurt and Blair Brown.