) is an antimetabolite drug that is widely used in the treatment of various cancers, including colorectal cancer and breast cancer. Several modulation strategies have been developed to improve the therapeutic effectiveness and cytotoxicity of 5-FU treatment. Although 5-FU is considered to be one of the safest chemotherapeutic agents, its toxicity can cause severe side effects (including fever, fatigue, and nausea) and toxic effects (including leukopenia and anaemia). Moreover, 5-FU treatment frequently results in the development of chemoresistant tumour cells. Use of carrier materials could ideally allow for a targeted release in the human body, increasing cytotoxicity while at the same reducing the amount of drug required for effective treatment, thereby limiting side effects and resistance development. The variety of materials that have been investigated as potential 5-FU delivery vehicles is the subject of dedicated review articles. Organic materials that have been proposed for this purpose include polymer microspheres and functionalised block copolymers that release 5-FU under UV irradiation, among many other systems. Examples from the field of inorganic (nano)materials include functionalised silica nanoparticles, 9,10 layered hydroxyapatite, as well as purified natural clay minerals (e.g., montmorillonite ) and clays modified with organic surfactants or other agents. Zeolites are crystalline inorganic materials whose structures are built up by a framework of corner-sharing TO4 tetrahedra. Most natural zeolites and the majority of synthetic zeolites have an aluminosilicate composition (T = Si, Al), resulting in a negative framework charge that is balanced by extra-framework cations or framework protons. However, neutral-framework allsilica zeolites and zeolite-like materials having other elements on the T sites have also been reported. The presence of accessible cavities or channels is a key feature of zeolite crystal structures, and the arising intrinsic porosity is pivotal for their large-scale use in catalysis, ion exchange, and separation processes. Besides these established applications, zeolites have also received considerable interest as potential drug delivery materials, along with other possible applications in medicine. With regard to the specific task of 5-FU delivery, Datt et al. studied the storage and release of 5-FU from Y zeolite samples (FAU framework type ) having Si/Al ratios of 2.5, 15, and 30. They observed similar loadings for all three samples, on the order of 0.1 g 5-FU per gram of zeolite, but rather different release characteristics, with the most Al-rich sample (Si/Al = 2.5) releasing only a small fraction of the adsorbed 5-FU under physiological conditions. In contrast, the more Si-rich samples released more than 50% within a few minutes. Al-NMR spectroscopy provided evidence for a binding of 5-FU to extraframework aluminium (EFAL) sites, which were most abundant in the most Al-rich sample. Subsequently, a number of other authors studied the 5-FU delivery properties of various zeolites. Neves, Baltazar and co-workers investigated sodium-exchanged zeolite Y (NaY) and compared it to other systems including Linde type L and Linde type A zeolites (LTL and LTA framework, respectively) and ZSM-5 (MFI framework). They also demonstrated the cytotoxicity of the 5-FU@zeolite composites to different cancer cell lines in cell viability studies, whereas the pristine zeolites were shown to be non-cytotoxic. Spanakis et al. compared the 5-FU release behaviour of zeolite NaX (FAU framework) and zeolite beta (BEA framework) and employed molecular dynamics (MD) simulations using a classical force field (FF) to explain the observed differences. Apart from commercially available synthetic zeolites, which can be relatively expensive, zeolites synthesised from inexpensive and widespread starting materials (metakaolin) and natural zeolites were also investigated as 5-FU carrier materials. Another avenue of research is constituted by the preparation and characterisation of functionalised zeolites and zeolite-containing nanocomposites. For example, it was shown that surface functionalisation of synthetic zeolites can enhance the bioavailability of encapsulated 5-FU. Magnetic nanocomposites of zeolites and Fe3O4 nanoparticles are of interest as they could be directed to the location of the tumour through application of an external magnetic field. Furthermore, the use of silver-exchanged zeolites as 5-FU carriers could help to prevent microbial infections in the tumour microenvironment due to the antimicrobial activity of Ag + cations. Looking beyond zeolites to other crystalline porous materials, metal-organic frameworks (MOFs) and MOF-containing nanocomposites have also been investigated as materials permitting controlled 5-FU delivery. Apart from their potential use as 5-FU carrier materials, zeolites could also be employed as adsorbents for the selective removal of 5-FU from wastewaters. While little focus has so far been placed on 5-FU in this context, a number of experimental investigations have dealt with the removal of other pharmaceutically active ingredients from wastewaters using hydrophobic high-silica zeolites. Although 5-FU is not commonly ranked among the pharmaceuticals of most concern with regard to their environmental impact, it has been identified as a priority cytostatic drug for environmental monitoring studies due to its reported persistence and ecotoxicity. In addition to occasional reports of low levels of 5-FU (< 10 ng L -1 ) in wastewater treatment plant influents, 5-FU has been detected primarily in hospital effluents, in at least one case in high concentrations exceeding 100 µg L-1. The toxicity (including genotoxicity) of 5-FU, alone and in mixtures, has been investigated for various aquatic organisms, and estimations of the arising environmental hazard potential generally agree that its potential environmental impact is non-negligible. This highlights the need to develop efficient removal strategies from contaminated waters, especially hospital effluents. Among other technological options, adsorption-based processes using activated carbons have been proposed for 5-FU removal. While they are more expensive to produce than activated carbons, hydrophobic zeolites might constitute an interesting alternative due to the reduced pore blockage by co-adsorbed natural organic matter and good adsorbent regeneration properties. Due to their narrow pore size distribution, they are especially well suited for the highly efficient removal of molecules that fit well into the pores.