Though one of the most inveterate smokers I ever met with, he gave up his cigar, because she said, one day, she hated the stale smell of it in his clothes. (18.104.22.168)
Franklin Blake loves Rachel so much that he's willing to give up smoking cold turkey just because the smell annoys her.
He slept so badly, after this effort of self-denial, for want of the composing effect of the tobacco to which he was used, and came down morning after morning looking so haggard and worn, that Miss Rachel herself begged him to take to his cigars again. (22.214.171.124)
Of course, Franklin Blake has been smoking for years, so giving up smoking cold turkey makes him feel awful. Addiction has that effect on people.
My head was by this time in such a condition, that I was not quite sure whether it was my own head, or Mr Franklin's. […] I retired to my own room; and I solaced myself with the most composing pipe of tobacco I ever remember to have smoked in my life. (126.96.36.199)
Even Gabriel Betteredge has an addiction: like Franklin Blake, he is addicted to tobacco, and smokes to calm himself down when he's worried.
The one effectual palliative in my case, is—opium. To that all-potent and all-merciful drug, I am indebted for a respite of many years from my sentence of death. But even the virtues of opium have their limit. (188.8.131.52)
Ezra Jennings takes opium to numb the pain caused by his illness. He's never specific about what his illness is, only that it's terminal, and he takes opium in order to live long enough to save money for the girl that he wanted to marry back before his reputation was ruined.
'Stop!' he said. 'You have suggested more to me than you suppose. Have you ever been accustomed to the use of opium?' (184.108.40.206)
Franklin Blake has been describing the disappearance of the Moonstone and his own apparent involvement in its disappearance. His description makes Ezra Jennings leap immediately to the idea that he might have taken it while under the influence of opium.
'This is a marked day in your life, and in mine,' he said, gravely. 'I am absolutely certain, Mr Blake, of one thing—I have got what Mr Candy wanted to say to you this morning, in the notes that I took at my patient's bedside. Wait! that is not all. I am firmly persuaded that I can prove you to have been unconscious of what you were about, when you entered the room and took the Diamond.' (220.127.116.11)
Ezra Jennings is so convinced that Franklin Blake might have taken the Diamond while under the influence of opium that he tells him that he can "prove" it.
'Betteredge was perfectly right, Mr Blake. When smoking is a habit, a man must have no common constitution who can leave it off suddenly without some temporary damage to his nervous system.' (18.104.22.168)
Addiction was a relatively new idea when The Moonstone was written (in 1868). Before, many people didn't recognize it as a medical condition at all. So Ezra Jennings's remark that it's difficult to quit smoking cold turkey wasn't quite as obvious as it sounds to us.
'The common error about opium, Mr Blake! I am, at this moment, exerting my intelligence (such as it is) in your service, under the influence of a dose of laudanum, some ten times larger than the dose Mr Candy administered to you. But don't trust my authority—even on a question which comes within my own personal experience. I anticipated the object you have just made: and I have again provided myself with independent testimony, which will carry its due weight with it in your own mind, and in the minds of your friends.' (22.214.171.124)
Ezra Jennings has to take laudanum (a mixture of opium with alcohol) to treat the pain of his disease. But he's used to taking it, so his tolerance is higher. Franklin Blake, on the other hand, never takes it, so when he took a tiny amount on the night of Rachel's birthday party, it had a dramatic effect on him.
'At the passage which I have marked, you will find that when De Quincey had committed what he calls "a debauch of opium", he either went to the gallery at the Opera to enjoy the music, or he wandered about the London markets on Saturday night, and interested himself in observing all the little shifts and bargainings of the poor in providing their Sunday's dinner. So much for the capacity of a man to occupy himself actively, and to move about from place to place under the influence of opium.' (126.96.36.199)
Ezra Jennings uses Thomas De Quincey's Confessions of an English Opium Eater, a famous, mostly autobiographical account of opium use and addiction, as evidence of how opium can affect a person.
'In the spiritualized intoxication of opium, you would do all that. Later, as the sedative action began to gain on the stimulant action, you would slowly become inert and stupefied. Later still you would fall into a deep sleep. When the morning came, and the effect of the opium had been all slept off, you would wake as absolutely ignorant of what you had done in the night as if you had been living at Antipodes.' (188.8.131.52)
Ezra Jennings tells Franklin Blake that the initial effect of opium would energize the user – he or she would only later fall asleep.