It’s quite possible that opium could be smoked in any sort of smoking pipe – or at least, an attempt could be made. There is a specific form of pipe, though, designed solely for vaporizing opium using an external heat source. Since many sorts of pipes are frequently (and understandably) mistaken for ‘opium pipes’ in film, print, and on the web, it may be helpful to clarify matters.
Opium Pipes
There are two cultural forms of ‘true’ opium pipe, those instruments built expressly for the purpose of vaporizing just opium. The differences in overall design largely come down to what is used as a steady heat source – a vegetable oil lamp, or a piece of charcoal.

The Chinese style of opium pipe, called the yen tsiang, or ‘smoking pistol’, and its accouterments are the focus of this website. A typical Chinese pipe consists of a hollow shaft of bamboo, ivory, or other material, about 35-50 cm long, with a fitting for a detachable pipe bowl at the end or partway down the shaft. A pipe bowl, about the size and shape of a doorknob, is typically made of clay or porcelain, and is hollow, with a tiny hole at the top for the drug, which is vaporized over an oil lamp.
This style of pipe was used throughout East Asia, and also wherever in Europe and America that culture of opium-smoking permeated. There are variations, for example a more rudimentary form of Chinese-style pipe used in remote, rural areas has a shorter shaft and a bowl fitted directly to the end, without a metal fitting. (To see the Chinese pipe in more detail, including its shorter variations, visit Anatomy of an opium pipe.)

The Persian style of opium pipe, called a vafoor, is somewhat similar. It typically consists of a hollow shaft of hardwood, shorter than a Chinese pipe, with a clay bowl at the end with a brass fitting. The opium is vaporized using a smoldering piece of charcoal, held with tongs close to the bowl.
Some sources point out that in the Persian opium-smoking culture, another type of pipe existed that was more like the Chinese pipe, as it was designed for use over oil lamps.
Hookahs & East Asian Water Pipes
There are two forms of water pipe that are often labelled as opium pipes. The hookah is a larger pipe, with a water-filled base and a long stem, often with a hose connecting the base to the mouthpiece:

Hookahs are typically used to smoke shisha, a wet mixture of tobacco, molasses, and other ingredients. While it’s certainly possible opium could have been added to some hookah smokers’ mixtures of choice, it isn’t really a purely opium-smoking device.
The Chinese water pipe also gets mistaken for an opium pipe quite often. Smaller than the hookah, but operating on the same principle with water filling its base for filtration, these were typically used to smoke tobacco:

Some of the confusion probably comes from the fact that tobacco pipes were frequently used in the same environs as opium pipes, so a picture of an “opium den” would often have some of these tobacco pipes in the scene as well. Here, the man on the right is smoking an opium pipe, while the woman on the left is smoking the Chinese water pipe:

Another form of water pipe are these ceramic or wooden vessels, often represented as opium pipes and found typically in Vietnam and Thailand. I haven’t seen any evidence that these are actually for smoking opium – their design and form factor seem to be a variation on the Chinese water pipe seen above, and museums in the region label them as being for tobacco or cannabis:

There is an additional type of water pipe that is still often used today in Southeast Asia, which is a long bamboo cylinder that resembles a bong. This is typically used for smoking tobacco, like this Hani man in China. (Credit: Shiran De Silva – video)

Kiseru
Another form of pipe that often gets mistaken for an opium pipe is the Japanese Kiseru. This was used to smoke a tiny pinch of tobacco, and was the most popular way to smoke in Japan before the 20th century.

Other Tobacco Pipes
Many other unusual forms of tobacco pipe are often mistaken for opium pipes. Here is an image that gets frequently used on the internet as a picture of “Opium Smokers”:

These two are actually smoking a form of tobacco pipe that was popular in Europe during the 19th century, which has been called the gesteckpfeife, or the Tyrolean, Student, or Regimental pipe:

Souvenir Pipes & Auctioneer’s Mistakes
There are many sorts of pipes – all over the internet, and all over marketplaces throughout Asia – that are basically replicas or souvenirs, labelled as “opium pipes” but in reality nothing like the actual pipes used in old-fashioned opium dens. Small metalwork pipes like these are very common:

Even fancy auctioneers sometimes get things wrong, misidentifying items as “opium pipes” seemingly by the seat of their pants. For example, this isn’t an “Argentinian opium pipe” as its auctioneer claimed. It’s a bombilla – a straw used for drinking yerba mate:

Replicas
There are many replicas that are quite similar to genuine opium pipes, in form and dimension. Some of these require close examination to determine whether or not they are the real thing – and some are completely authentic in every detail, but were made just yesterday. If you want to know more about a particular pipe, tool, or other opium artifact, I recommend reading further, or consulting an expert… or both!