The first person to send me a link on my blog is Anonymous but I thank that person. He or she sent me a link for http://www.drugscience.org.uk
which is an independant organisation that takes no funding from government. It does speak of harm reduction rather than abstension (which I prefer) but let's start with a drug that is not a class A and which seems to be mentioned the most, Cannabis. An extract from a page is here and the section is shown in its entirety.
I think the whole website gives a good balanced view and is up to date so recommend taking a look.
What are the potential harms of cannabis?
Most people consume cannabis by smoking it and most include tobacco in the mixture they smoke. The harms of tobacco smoke are well recognised but the harms of cannabis smoke are not. Analyses of the combustion products of pure tobacco and cannabis have shown them to be similar and cannabis smoke is inhaled more deeply than tobacco smoke (Iversen, 2008).
The potential harms of smoking cannabis are sometimes argued to be less than the harms of smoking tobacco cigarettes because the latter are smoked more regularly and for a longer period of a person’s life. However, cannabis joints are often mixed with significant amounts of tobacco and some regular users smoke tobacco cigarettes in the periods between smoking cannabis joints. The smoking of any tobacco-containing product can lead to dependence due to the addictive properties of nicotine.
It has long been recognised that cannabis (or more accurately THC) can cause temporary psychotic symptoms (Moreau, 1845; Weil, 1970). The risk of this is increased if the cannabis contains a high proportion of THC in relation to another ingredient of cannabis, cannabidiol, which may counteract the psychoactive effects of THC (Morgan & Curran, 2008; Bhattacharyya et al. 2010).
The THC content of cannabis has increased dramatically in recent years. Although it is well established that cannabis can cause transient psychotic symptoms in normally healthy individuals and negatively affect treatment outcome in patients with schizophrenia (Zammit et al. 2008) the idea that it can cause schizophrenia in healthy individuals is controversial (Nutt, 2009). What seems more likely is that cannabis can promote psychotic illness in individuals that are already vulnerable to this.
Cannabis has a very low-level of toxicity and presents a relatively low risk of dependency (ACMD, 2008). For these reasons, it is typically considered a relatively safe drug (Nutt et al. 2007). This is not to say that cannabis is harmless, only that its harms are relatively less serious than those associated with other drugs.
Studies have associated long-term cannabis use with poor educational achievement and psychological health (e.g., Macleod et al. 2004) but it is difficult to determine whether cannabis is a cause or effect of this. In a survey of 620 cannabis users, 43% reported that cannabis had probably (30%) or definitely (12%) caused or made worse a physical or mental health problem but users also rated cannabis as having the least serious negative effects (Carhart-Harris & Nutt, 2008). The most prevalent negative effect of cannabis reported by users is apathy (see Iversen, 2008).
What is the current legal status of cannabis?
Cannabis was classified in most countries in the late 1920s. In 1971, under the Misuse of Drugs Act, cannabis was made Class B. In 2002, The Advisory Council on the Misuse of Drugs (ACMD) recommended that cannabis be reclassified to Class C based on an assessment of its relative harms. This was implemented in 2004.
Based on fresh fears about the increasing potency of cannabis and associated mental health risks, at the request of the government, the ACMD carried out two reviews of the evidence on cannabis, in 2005 and 2008, advising on both occasions that cannabis remain Class C. Cannabis was reclassified to Class B in January 2009. Possession of Class B drugs is punishable by up to 5 years imprisonment and dealing or importation can result in 14 years imprisonment.
Advisory Council on the Misuse of Drugs (2008) Cannabis; classification and
public health. http://drugs.homeoffice.gov.uk/publication-search/