Bateman's Drops had been around since the 1720s and were prepared by various suppliers, hence the specification that these were Barclay's Bateman's Drops rather than anyone else's.
The main ingredients were aniseed, camphor and opium, so the drops would have at least a temporary effect and could be rather dangerous if swigged indiscriminately. Different suppliers had different recipes and the amount of opium varied considerably.
BARCLAY'S DR. BATEMAN'S PECTORAL DROPS—This Medicine has long been held in the highest estimation for all Rheumatic and Chronic complaints, in pains of the limbs, bones, and joints, for influenza, and in violent colds. The genuine Bateman's Drops, prepared by BARCLAY and SONs, if taken in time, are a great pre- ventive of fever, which too often arises from neglected colds. As a proof of the great efficacy of Barclays' Bateman's Drops in Rheumatism, the following cure is submitted to the public and every inquiry into the truth of the statement earnestly solicited:— Extract from a letter addressed to Mr. Hattley, Bury. Greenhalgh Moss, near Bury. Sir—In the beginning of last winter, I was suffering under a severe attack of Rheumatism, and being informed by my neighbour, Henry Lord, of the great benefit his wife had received from the use of Barclays' Bateman's Drops in a similar complaint, I was induced to try the same, and hav- ing purchased a bottle from your shop, I found the greatest relief, and before I had taken the fifth bottle, I was able to follow my employment, and continue in good health. I remain your obedient servant, ROBERT BOOTH. ***Be careful to ask for Barclays' Bateman's Drops, and observe that the names of BARCLAY and SONS are en- graved on the stamp. Price 1s. 1½d. and 2s. 3d. Source: The Derby Mercury, Wednesday 5th January, 1842. Note: The inconsistency of apostrophe placement (Barclay's/Barclays' ) is as shown in the original.